Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

A pyramid has an centre of gravity which is intentionally low. This is evidenced by it only being at a quarter height. I'm not saying there aren't issues with the technology, but it's not the best example.

I just wanted to palce the claim into context. To give it some scale. This is also what I've found:"San Francisco use about 6,500 MWh daily with around 800,0000 residents."So assuming that it is to store solar power, you would need to build 100 towers to make it through the night. And it has so many moving parts, that make it really unreliable.

I think the clear way to store energy is Power to gas (LNG). The round trip efficiency is not that great at the moment, at around 75%, but that is not important*. Storing gas is a solved problem. 1 cubic meter of LNG is about 600 cubic meter of natural gas, about 6000KWh. In a 30 foot container that is about 200MWh, or 8 of these towers. The entire concept is just silly if you compare it. This is 135000 cubic meter, or about 810000 MWh, enough to power the SF for 4 months.

*What is important is the total system cost. If you spend 2 EUR (including amortization) storing 1 EUR worth of electricity, you are doing it wrong**. What matters is the electricity cost at night. You can overcome efficiency problem with "just" more solar power. ** That is why the ie powerwall is a futile concept. It costs more to store the electricity than to buy it.

Hang on -- I may be missing something here. LNG is Liquefied Natural Gas. The actual power (eventually used for heating, generating electricity etc.) comes from the natural gas, i.e. a fossile fuel, right?

One applies additional energy to liquidify it -- but that is not to store that additional energy, but just to make the natural gas more compact for transportation?

I may have this wrong, in which case, please correct me. Otherwise, while liquefied gas certainly has its uses, you seem to mention it in an incorrect context here: It is not used to store electrical energy, generated from wind or solar.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.Power to gas (P2G) is not done in the industrial scale, but there is a 100 MW plant being built in Germany. I think others will follow. And methane can be used in many other ways than just power generation. My favorite part about P2G is that it is actually reverses the CO2 emissions and global warming.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

Way back in the day, before electrical power of any scale was really practical, the dock at Liverpool had a clever hydraulic energy storage scheme for operating its cranes and winches.

It looked kind of like pumped storage writ small, but with the trick that the accumulator towers were really giant hydraulic rams that lifted large weights to allow high working pressures without needing the towers to be overly high... Prime power was steam plant in a few engine house locations around the dock.

Did it work? Yes, it did, but it was far more about peak power demand then bulk energy storage, and we have easier ways to do that today.

There are lies, damned lies, statistics - and ADC/DAC specs.Gliding aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".Having fun doing more, with less

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

The point is that we can store massive amount of LNG and it is probably the cleanest thing to burn. There is already a gas network built up and we use a lot for heating. Power plants are there and transportation can be converted to use it. Not just cars, but cargo ships for example. So there is infrastructure to use it, and we have the means to generate it, and store it.And CO2 scrubbing is possible. It might be "more expensive" than other methods, but the point is that the cost is energy. All these problems can be offset by just installing more panels.

So you pyrolyze wood to make wood gas, burn that gas to get CO2, then invest energy to make methane which you can burn later on? Well sure, but why not use wood and wood gas directly?

Because using wood that way isn't "renewable"/"CO2 neutral" according to the climate agreements?

Actually, wood isn't very compact, so converting the wood gas to methane (which is already widely used in e.g. buses) would be simply a fuel refinement process.

I do know that CO2 sequestration from ambient air is nontrivial, and typical concentrations (0.04% per volume) are so low that the methane-generating processes cannot realistically rely on CO2 from ambient air.

Once exporting begins - it seems to me that a country now has to allow it - to the higest bidder, not to any favored group, like their own people, regardless of its impacts. It likely wouldnt matter where it came from, cutting down living forests to create wood gas may seem like a bad idea to us but that doesnt likely matter, just sayin.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

The point is that we can store massive amount of LNG and it is probably the cleanest thing to burn. There is already a gas network built up and we use a lot for heating. Power plants are there and transportation can be converted to use it. Not just cars, but cargo ships for example. So there is infrastructure to use it, and we have the means to generate it, and store it.And CO2 scrubbing is possible. It might be "more expensive" than other methods, but the point is that the cost is energy. All these problems can be offset by just installing more panels.